Various Methods of Moulding. 5 :ings, ribbed ;as from the .d and loamj easures, that sand should ogether with poses. The >f silica in its mch as 93 or :r substances. ) much when , it should at .ssage of airr [ entering it. sous*) with a It is ground , horse dung, rosity. Dck sand and i, for the use blast-furnace Derfectly dry. hods: Green In green and dry sand moulding, patterns are generally used; but in loam moulding, which is only employed for objects of regular form, the mould is struck out by means of a template, \ and built up by the moulder himself * Green Sand is the geological name of a sand of very fine texture. It appears black in the foundry because it is mixed with a proportion of coal and charcoal dust; it is damped each time that it is used. This is the most general method of moulding, with castings not likely to warp too much by the more rapid cooling. (See Appendix //.,/. 779.) v Dry Sand is a mixture of old loam with an addition of rock sand. It is so called because, after the pattern is moulded, the sand is dried by means of fires hung in pans or trays over the moulds. It is firmer and more suitable for the support of long castings, such as pipes, columns, and large fly-wheels than green sand is, and will produce finer castings, with less fear of pieces of sand being torn away by the flow of the metal. If pipes are moulded in green sand, the tendency is to uneven thickness in the castings, through sagging of the sand. • Loam Moulding, as we have said, does not require a pattern, the mould being struck in the pasty loam (the latter being mixed with water) by means of a rotating or sliding template, called a * striking-board. Thus the core of a large cylinder, is built up in brickwork, and then covered with a layer of loam, which is smoothed by a rotating striking - board (see Fig. 3), much as a plasterer would work the cornice of a house ceiling. Cubical moulds, such as those for condensers, may also be worked in loam. The simplest moulding done in green sand is called Open Sand Moulding, and consists in laying the pattern in the sand on the foundry floor, withdrawing, and then pouring in the metal, a cover not being used. This is the method employed for such common objects as moulding boxes (see Fig. 4). wank.